Systems for providing a flow of air for engine cooling in automotive vehicle or like applications are generally known. The design of these engine cooling systems is constrained by flow and thermal requirements, design of related systems and equipment, and size and space constraints within the engine compartment. For example, in an automotive (or like) application having an air conditioning module, a condenser for the air conditioning module is likely to be positioned in relatively close proximity to a heat exchanger (e.g. radiator or the like) provided for engine cooling, both being located at or near the front of the engine compartment (and a potential supply of cooling air). In a typical arrangement of this type, the condenser and heat exchanger may be provided with a flow of cooling air supplied by a fan which is mounted in a fan shroud assembly in front of the condenser and heat exchanger. The fan (typically powered by an electric motor) is configured to force cooling air onto and through the condenser and heat exchanger from the front of the engine compartment. One type of exemplary arrangement of a fan shroud assembly is shown in U.S. Pat. No. 5,244,347 issued to Gallivan et al. (and commonly assigned to the owner of the present application), which is incorporated by reference herein.
It is known to include one or more air doors in order to facilitate a flow of supplemental cooling air to the engine in addition to that ordinarily provided by the fan itself. The air door assembly is typically designed to allow supplemental cooling air to flow through the engine compartment as the vehicle increases in velocity. In a common arrangement each air door fits within a corresponding opening, the door being pivotally mounted across the top of the opening by a hinge and hanging vertically from the top of an opening. According to this known mounting arrangement, the door will open with respect to the opening when the air flow on the door (which is a function of the air velocity which in turn relates to the velocity at which the automobile is traveling) develops sufficient force (i.e. pressure action over a surface area) to overcome the forces acting to maintain the vertically-hanging door in a closed state.
According to this known arrangement, the velocity at which the door will tend to open (and thereby allow the flow of supplemental cooling air into the engine cooling system) is dependent upon such factors as the weight of the door, the effective frontal surface area and shape of the door, inertia and friction effects, and the like. Nevertheless, due to the effects present in this known arrangement, it is unlikely that the door can be maintained consistently in a fully opened state (e.g. horizontal orientation) as to maximize the flow area for supplemental cooling air. Moreover, the fan shroud assembly, condenser, heat exchanger and other equipment must be positioned to allow clearance and avoidance of interferences or obstructions with the fully-opened air door. In order to maintain a compact profile, it may be necessary to make a trade-off between a desired size of the door (and its corresponding opening) and placement and overall design of a compact engine cooling system. Furthermore, this known arrangement is not well-suited to provide for a discrete transition of the door between a fully closed state and fully open state, as the door tends to open gradually as the velocity of the air flow increases.
Accordingly, it would be advantageous to have an air door arrangement that is of a compact and yet sufficiently large open area, that does not give rise to interferences with other equipment or systems, and that can be accommodated with air doors of a variety of materials and shapes. It would also be advantageous to have a ram air door arrangement that can be adapted to provide for a discrete transition of the door between a fully closed state and a fully open state at a particular threshold air velocity (and also provides for a hysteresis effect). It would further be advantageous to have an air door mounting arrangement wherein the hinge point is moved from the top of the opening (as in the known mounting arrangement) to a lower position within the opening to achieve certain design advantages. It would further be advantageous to have an air door that is designed for relatively simple assembly and low cost manufacture.